This invention generally relates to toolholders having passive coolant inducers, and is specifically concerned with a toolholder having an impeller-type coolant inducer that receives, pressurizes, and conducts an external stream of coolant to a cutting tool without the need for mechanical containment or other interfaces between the toolholder and the source of coolant.
Toolholders having coolant supply systems are well known in the prior art. Such toolholders generally comprise a rotatable toolholder body having a shank for coupling the toolholder to a rotatable drive shaft, an adapter for connecting a cutting tool such as a drill or milling head to the shank, and a coolant passageway for conducting a stream of pressurized, liquid coolant at the interface between the cutting tool and a workpiece. Because of the relative movement between the body of the toolholder and the source of pressurized coolant, the pressurized coolant is typically delivered to the toolholder by means of a conduit that is connected to one of two interfitting and relatively movable components of a coupling. The other of the two interfitting and relatively movable components is connected to the body of the toolholder. Such couplings include dynamic fluid seals between their two interfitting components to prevent unwanted leakage of the pressurized coolant during the rotation and operation of the toolholder.
While toolholders having such coolant systems have proven their ability to operate satisfactorily in many types of machining operations, the applicant has observed that a number of problems arise from the use of a dynamically sealed coupling to contain the coolant transmitted by the stationary coolant supply into the rotating body of the toolholder. For example, the seals necessary to contain the pressurized coolant in such a coupling generate significant amounts of friction during a machining operation, thereby lowering the power transmission efficiency between the drive shaft and the cutting tool. This problem has become highly exacerbated by the current and growing demand for high speed machining operations, wherein the toolholder is rotated at substantially higher rpms. Frictional forces increase exponentially with speed. Hence, the doubling or trebling of the rotational speed of the toolholder can increase the frictional forces between the fluid seals by factors between four and nine. Such greatly increased frictional forces not only interfere with power transmission, but greatly accelerate the wear on the fluid seals, thereby necessitating more frequent replacement, which in turn translates into a larger amount of expensive downtime for the tool. Moreover, the fluid-tight couplings used in conventional coolant-supplied toolholders are expensive components which must be manufactured in accordance with relatively tight tolerances. Finally, the installation of the conduits, and the rigid connections between the coolant carrying conduits and the fluid-tight couplings all necessitated by the need for mechanical containment seriously impairs the overall flexibility of the tooling system, as the coolant "plumbing" must be disconnected and reconnected every time a replacement toolholder is connected to the drive shaft.
While the applicant is aware of an alternative coolant system disclosed in U.S. Pat. No. 5,183,363 which eliminates the need for dynamic seals per se, such a system still requires the provision of a stationary, annular member that is closely spaced around the periphery of the tool spindle (i.e., about 5/1000 of an inch) in order to effectively distribute a supply of coolant around the periphery of the spindle where it can ultimately flow into one end of a helical passageway present in the spindle body. Hence, while such an alternative design can eliminate the friction associated with dynamic sealing components used in more conventional coolant-supplied toolholders, the need for stationary, closely fitting coupling members is still present, along with the aforementioned lack of flexibility associated with the connection and disconnection of a rigid coolant plumbing system every time the toolholder is changed.
Clearly, there is a need for a toolholder having a coolant supply that not only obviates the need for sealing components, but any mechanical containment whatever in the interface between the stationary coolant supply and the rotating body of the toolholder. Preferably, such a design should be easy and inexpensive to manufacture, and readily applicable to a variety of tool-mounting adapters. Finally, the coolant system associated with such a toolholder should not require the time-consuming connection and disconnection of cumbersome coolant plumbing systems to the body of the toolholder whenever the toolholder is installed or replaced.